There are a number of assays and sensors for the detection of the presence and/or concentration of specific substances in fluids and gases. Many of these rely on specific ligand/antiligand reactions as the mechanism of detection. That is, pairs of substances (i.e. the binding pairs or ligand/antiligands) are known to bind to each other, while binding little or not at all to other substances. This has been the focus of a number of techniques that utilize these binding pairs for the detection of the complexes. These generally are done by labeling one component of the complex in some way, so as to make the entire complex detectable, using, for example, radioisotopes, fluorescent and other optically active molecules, enzymes, etc.
Other assays rely on electronic signals for detection. Of particular interest are biosensors. At least two types of biosensors are known; enzyme-based or metabolic biosensors and binding or bioaffinity sensors. See for example U.S. Pat. Nos. 4,713,347; 5,192,507; 4,920,047; 3,873,267; and references disclosed therein. While some of these known sensors use alternating current (AC) techniques, these techniques are generally limited to the detection of differences in bulk (or dielectric) impedance.
There are a variety of nucleic acid biosensors currently known. These include nucleic acid biochips based on fluorescent detection; see for example materials developed by Affymetrix (including, but not limited to, 5,800,992, 5,445,934, 5,744,305, and related patents and materials), Nanogen (including, but not limited to, 5,532,129, 5,605,662, 5,565,322 and 5,632,957 and related patents and materials), Southern (EP 0 373 023 B1) and Synteni/Incyte (WO 95/35505 and related patents and materials).
Similarly, electronic detection of nucleic acids using electrodes is also known; see for example U.S. Pat. Nos. 5,591,578; 5,824,473; 5,705,348; 5,780,234 and 5,770,369; U.S. Ser. Nos. 08/873,598 08/911,589; and WO 98/20162; PCT/US98/12430; PCT/US98/12082; PCT/US99/10104; PCT/US99/01705, and PCT/US99/01703 and related materials.
However, to date none of these methods have been used in highly parallel systems to allow biochip multiplexing. Accordingly, it is an object of the present invention to provide devices and methods for multiplex analysis of biochips, particularly nucleic acid biochips.